1. Field of the Invention
The present invention relates to capacitors and in particular to capacitors integrated in a semiconductor substrate.
2. Description of the Related Art
Integrated capacitors are an important ingredient in many semiconductor devices or integrated circuits. For example, integrated capacitors are used in PIN switches or microphone filters. Moreover, integrated capacitors are used in memory cells in conjunction with a transistor in order to store digital information in the memory cells.
In order to obtain high area capacity, i.e. low consumption of chip area per supplied capacity, of the capacitors on the chip, trench capacitors are used, in which the capacitor is housed in a trench of the substrate. By the use of trenches, the depth of the substrate is utilized to provide areas for the formation of the capacitors, whereby high area capacity results.
EP-0 479 143 A1 for example describes a trench capacitor DRAM memory with voltage field insulation. The trench capacitor comprises a plurality of capacitor plates created by a dielectric in the trench formed in a substrate. Both capacitor plates formed of doped semiconductor material are housed in the trench and extend from the trench as thin layers. A further layer disposed nearest to the sidewall of the trench functions as a field-shielding layer. A plurality of sacrificial layers are used and formed over the structure. The other plate of the trench capacitor is also connected to a source/drain area of a transistor via a connection layer.
The above-described, known trench capacitor comprises capacitor plates formed as thin layers, because both the first and the second capacitor plates are in the trench. This is disadvantageous in that very high dopings are required each for achieving low series resistances for the capacitor plates formed as thin semiconductor layers. Furthermore, the applying of layers is connected to high expenditure. In addition to the capacitor dielectric, an electric insulation is applied at the sidewalls of the trench.